How to improve the life of photovoltaic inverters by heat dissipation?

But in fact, the inverter is not just an invertor, but a safety manager of the photovoltaic power station. The inverter also undertakes system-level functions such as monitoring and protection of the photovoltaic array and the power grid, protection against the external environment, and human-computer interaction.

Why does the inverter need heat dissipation?

As a power electronic device, the inverter faces the challenges brought by temperature like all electronic products.

Of all electronic product failures, up to 55% are caused by temperature.

The electronic components inside the inverter are also very sensitive to temperature. According to the 10-degree rule in reliability theory, the life span is halved for every 10-degree increase in temperature from room temperature, so the inverter heat dissipation design is very important.

Several ways to dissipate heat from the inverter

The inverter heat dissipation system mainly includes radiator, cooling fan, thermal grease and other materials.

Currently, there are two main ways to dissipate heat for inverters: natural cooling and forced air cooling.

1) Natural cooling

Natural cooling refers to the process of heat dissipation from local heat-generating devices to the surrounding environment to achieve temperature control without using any external auxiliary energy. This usually includes three main heat transfer methods: conduction, convection and radiation, among which natural convection is the main method of heat transfer.

Natural heat dissipation or cooling is often suitable for low-power devices and components that do not require high temperature control and have low heat flux density, as well as sealed or densely assembled devices where other cooling technologies are not suitable (or necessary).

Most manufacturers of mainstream single-phase inverters and three-phase inverters below 20kW on the market currently use natural cooling.

2) Forced air cooling

Forced air cooling is mainly a method of forcing air to flow around the device with the help of fans, thereby removing the heat emitted by the device.

This method is a heat dissipation method that is easy to operate and has obvious effects.

This cooling method can be used as much as possible if the space between components within the assembly is suitable for air flow or for mounting a local heat sink.

The method of improving the heat transfer capacity of this forced convection is to increase the heat dissipation area and generate a relatively large forced convection heat transfer coefficient on the heat dissipation surface. Increasing the heat dissipation area of ​​the radiator surface to enhance the heat dissipation of electronic components has been widely used in actual engineering.

In engineering, fins are mainly used to expand the heat dissipation area of ​​the radiator surface to achieve the purpose of enhancing heat transfer. The choice of radiator material itself has a direct relationship with its heat dissipation performance.

At present, the material of the radiator is mainly copper or aluminum, and its extended heat exchange surface is made by processes such as folded fins/stamped thin fins, etc.

3) Comparison of two heat dissipation methods

Natural heat dissipation has no fan and low noise, but the heat dissipation speed is slow, and is generally used for low-power inverters;

Forced air cooling requires fans, which are noisy but can dissipate heat quickly. They are generally used for high-power inverters.

For medium power string inverters, both methods are available.

Through the comparative experiment of heat dissipation capacity of string inverters, it is found that for string inverters with power levels above 50kW, the heat dissipation effect of forced air cooling is better than that of natural cooling. The temperature rise of key components such as capacitors and IGBTs inside the inverter is reduced by about 20°C, which can ensure the long life and efficient operation of the inverter.

However, the temperature of the inverter using natural cooling will rise and the life of the components will be shortened.

Forced air cooling also uses two types of fans: high-speed fans and medium-speed fans.

Using a high-speed fan can reduce the size and weight of the radiator, but it will increase noise and shorten the life of the fan;

With a medium speed fan, the radiator is slightly larger, but at low power, the fan does not turn;

At medium power the fan runs at low speed.

The reality is that the inverter does not run at full power for very long, so the fan life can be very long.

Latest cooling technology

With the continuous development of electronic technology, inverters have made great progress in heat dissipation:

(1) Chamber management: The components in the inverter that are most susceptible to temperature are op amps, sensors, electrolytic capacitors, etc. Inductors, cables, power switch tubes, etc. are relatively resistant to high temperatures. The heat-generating components can be isolated by chambering, and the heat-generating components, such as inductors, can be placed outside the inverter to reduce the temperature inside the chassis. At the same time, an integral shell structure can be used, with the radiator and the shell directly and tightly connected, allowing the aluminum alloy shell to dissipate heat through two paths, thereby achieving the effect of reducing the temperature of the components and the internal temperature of the inverter, ensuring a longer service life of the components and the inverter.

(2) Heat dissipation simulation technology: The simulation software can be used to simulate the thermal conditions of the system more realistically. During the design process, the operating temperature of each component can be predicted. In this way, the unreasonable inverter structure layout can be corrected, thereby shortening the design development cycle, reducing costs, and improving the first-time success rate of the product.

(3) Application of new heat dissipation materials: such as steel radiators, aluminum alloy radiators, copper radiators, copper-aluminum composite radiators, steel-aluminum composite radiators, stainless steel radiators, etc.

(4) New heat pipe cooling technology: Heat pipe is a new type of heat transfer element with extremely high thermal conductivity. It transfers heat by evaporating and condensing liquid in a fully enclosed vacuum tube. It uses fluid principles such as capillary absorption to achieve a good cooling effect. It has the characteristics of extremely high thermal conductivity, good isothermal properties, the heat transfer area on both sides of the hot and cold sides can be changed arbitrarily, heat transfer can be carried out over long distances, and the temperature can be controlled.

Pay attention to heat dissipation when installing the system

The inverter itself is a heat source, and all the heat must be dissipated in time. It cannot be placed in a closed space, otherwise the temperature will rise higher and higher.

The inverter should be placed in a well-ventilated space and avoid direct sunlight as much as possible.

When multiple inverters are installed together, sufficient distance should be left between them to avoid mutual influence.